HIV Prophylaxis for Partner Cuts Transmission

by Michael Smith Michael Smith North American Correspondent, MedPage Today
March 06, 2012

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These studies were published as abstracts and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

This study found that pre-exposure prophylaxis for the HIV-negative partner of an HIV-infected person successfully reduced transmission of the virus compared to placebo; the trial was halted early.

Note that a separate analysis of a cohort from the larger trial found that HIV-negative partners who became HIV-positive were significantly less likely to have tenofovir detectable in their blood at the seroconversion visit than those who were also in the active treatment arms but did not seroconvert.

SEATTLE -- Giving anti-retroviral drugs to HIV-negative people can reduce their risk of acquiring the virus from an HIV-positive partner, a researcher said here.

In a large randomized controlled trial in Africa, this type of pre-exposure prophylaxis, or PrEP, cut the risk of infection by up to 75% compared with placebo, according to Jared Baeten, MD, of the University of Washington in Seattle.

The so-called Partners PrEP study is "clearly proof of concept" that treating the uninfected partner in a heterosexual couple can be a good approach to prevention, Baeten told reporters at the annual Conference on Retroviruses and Opportunistic Infections.

The trial is a mirror image of the major study reported last year – the HPTN 052 trial – that found that treating the infected member of such couples reduces the risk of transmission by more than 90%.

Given those findings – and the increasing desire of physicians to treat HIV-positive people as early as possible – the results of Baeten's study may fall on stony ground.

But Baeten told MedPage Today he thinks there will be a place for treatment of the negative partner.

Taken together, the two studies show "a high degree of protection with the use of anti-retrovirals," he said.

But in the heterosexual epidemics in much of the developing world, he said, people face "difficult choices about individual treatment, individual risk, and risk decision making, often related to the desire for pregnancy."

When, for one reason or another, the HIV-positive partner can't start treatment or doesn't want to start, offering therapy to the other partner makes sense, he said.

In a discordant partnership, it's already part of recommendations that the HIV-positive partner be treated, commented Wafaa El-Sadr, MD, of Columbia University in New York City, who was not part of the study but who chaired a press conference at which details were presented.

But she concurred with Baeten that there are likely to be cases where treating the negative partner is the right choice. For instance, she told MedPage Today, "they may not be confident the positive person is taking their medicine."

The placebo arm of the Partners PrEP study was halted abruptly last July by the data monitoring committee, when it became apparent that there was a markedly increased risk to participants in that arm, Baeten noted.

He presented preliminary results in Rome at the meeting of the International AIDS Society and is giving the final numbers here.

Overall, he noted, the study enrolled 4,758 couples in which the HIV-positive partner was not yet eligible for treatment, according to local guidelines.

The uninfected partners were randomly assigned to get a daily dose of tenofovir (Viread), tenofovir plus emtricitabine (Truvada), or placebo. As usual in such trials, all participants got a range of other prevention measures, including counseling and free condoms.

After the randomization, 82 people acquired HIV, including 17 in the tenofovir arm, 13 in the tenofovir/emtricitabine arm, and 52 in the placebo arm.

Those differences meant that, compared with placebo, tenofovir reduced the risk of HIV by 67% and tenofovir/emtricitabine by 75% (P<0.0001 for both), Baeten reported.

The protective effect in the two active drug arms was numerically but not significantly different, and both medications worked equally well in both men and women, he noted.

There also was no apparent risk of resistance, he said, with no resistance to either drug detected among patients who acquired HIV after starting the study drug.

Among eight volunteers who had an acute – and therefore undetectable – infection when they started the study, only two developed a resistance mutation, Baeten noted.

Volunteers who acquired HIV while on one of the study drugs were compared with a cohort of participants who did not, using blood tests for the presence of tenofovir, according to Deborah Donnell, PhD, of the Fred Hutchinson Cancer Research Center in Seattle.

At the clinic visit where their seroconversion was detected, 35% in the tenofovir arm and 25% in the tenofovir/emtricitabine arm had evidence of tenofovir in their blood, Donnell told reporters.

In contrast, 83% of samples from uninfected controls in the tenofovir arm and 81% of samples from the tenofovir/emtricitabine arm had detectable tenofovir, she said.

She concluded that the presence of the drug is "highly correlated with protection."

The study was supported by the Bill and Melinda Gates Foundation. Gilead Sciences donated the study drug. Baeten and Donnell did not report any conflicts.

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